Method of preparing photosensitive surfaces

ABSTRACT

Photosensitive surfaces are formed on an electroconductive substrate by electrodeposition of zinc oxide from a system (suspension) containing photoconductive zinc oxide dispersed therein with an electrically insulating resin in a solvent for said resin.

United States Patent Shiota et al.

[ 1 Oct. 29, 1974 Filed:

METHOD OF PREPARTNG PHOTOSENSITIVE SURFACES Inventors: Shunsuke Shiota, Yokahama; Takao Sohtome, Tokyo, both of Japan Ricoh Company Ltd., Tokyo, Japan Nov. 6, 1972 Appl. No.: 303,865

Related U.S. Application Data Continuation of Ser. No. 42,501, June 1, 1970, abandoned.

Assignee:

Foreign Application Priority Data June 10, 1969 Japan 44-45633 U.S. Cl. 204/181 Int. Cl 801k 5/00 Field of Search 204/299 PE, 18 PC, 181

Primary ExaminerT. M Tufariello Attorney, Agent, or FirmCooper, Dunham, Clark, Griffin & Moran 57 ABSTRACT Photosensitive surfaces are formed on an electroconductive substrate by electrodeposition of zinc oxide from a system (suspension) containing photoconductive zinc oxide dispersed therein with an electrically insulating resin in a solvent for said resin.

7 Claims, No Drawings METHOD OF PREPARING PHOTOSENSITIVE SURFACES This is a continuation of application Ser. No. 42,501 filed June l, 1970 and now abandoned.

BACKGROUND OF INVENTION in the mixture. In this case, if necessary, an emulsifier ene is roller-coated on the support by means of a wire bar, bead, air knife, doctor blade, etc. However, a photosensitive layer formed by such methods is not uniform and compact. Furthermore, since the photosensitive layer so prepared is usually not uniform, the electrical properties are not completely satisfactory. For this reason, when it is attempted to produce a large number of copies of the same image, the results are usually unsatisfactory. Moreover, since the surface of the photosensitive layer is not smooth, the dry toner in the developing process becomes physically or electrostatically adhered to irregular spots on the surface of the photosensitive layer, consequently lowering the pictorial quality of the copied image.

It is an object of the present invention to provide a method of forming an electrophotographic photosensitive layer having excellent surface properties.

SUMMARY OF THE INVENTION The present invention relates to a method of forming a photosensitive layer'on an electroconductive support useful in electrophotographic copying by electrodeposition of the photosensitive layer or surface from a bath, as a disperse system (suspension), consisting of photoconductive zinc oxide, an electrically insulating resin and a solvent (dispersion medium).

The method of producing the photosensitive layer on a support by electrodeposition is as follows: Two electroconductive plates (electrodes) are immersed in a disperse system which has been prepared by intimately mixing photoconductive zinc oxide, an insulating resin and a solvent. A direct current voltage is applied to the plates and particles of zinc oxide which have adsorbed said resin are made to migrate to the one of the plates, thereby electrolytically depositing the zinc oxide particles on the plate. The particles of zinc oxide which have adsorbed the resin become either positively or negatively charged, depending on the solvent and the resin. Consequently, if the particles of zinc oxide are subjected to the influence of an electric field, they are deposited on either the positive electrode (anode) or the negative electrode (cathode) according to the nature of the electric charges of them.

The method in accordance, with this invention for forming a photosensitive layer is described in greater detail as follows: I

The zinc oxide disperse system (suspension) for the above-mentioned electrodeposition is prepared from photoconductive zinc oxide, an electrically insulating resin and a solvent (organic solvent or water). A sensitizer, emulsifier, etc., may be added to the disperse system, if necessary.

As the solvent mentioned above, an organic solvent such as toluene, xylene, tetrachloroethylene, ethylene dichloride, heptane, octane, methylene chloride, and

such as triethanolamine is added in the proportion of 0.l 0.4 percent by weight to the resinin use. A suitable disperse system for electrodeposition comprises g of zinc oxide, 15-30 g of a resin and 400-1 ,000 cc of a solvent.

When an organic solvent is employed as the solvent, any kind of electroconductive material may be used as an electrode. When water is employed as a solvent, a metal having low ionization tendency may be used. From the standpoint of handling and cost, an aluminum plate is especially useful as an electrode (electrodeposition plate) on which a photosensitive layer is deposited, and an aluminum plate or a graphite plate is used for the other electrode (opposite plate), As the properties of the photosensitive layer depends to some extent on the nature of the surface of the electrodeposition plate (electrode) upon which it is deposited, the'plate is subjected to preparatory treatments such as surface finishing, degreasing, etc. The plate upon which the photosensitive layer is to be electrodeposited is immersed in the bath in such a manner that one surface of the plate is left above the surface of the liquid while the opposite plate is immersed in the bath or liquid parallel with the plate to be electrodeposited. When said plate is cylindrical in form, the opposite plate is also to be made into the form of a cylinder or circular are. A tank for electrodeposition is made of an electroconductive material and said tank may be utilized as an opposite plate. The space between the electrodeposition plate and the opposite plate is preferably about 2 em but this is not limited.

As for the voltage applied between the electrodes, it is suitably 50-200 V/cm for the case where the dispersion medium is an organic solventsuch as mentioned above; On theother hand, for the case of water, the voltage of 2.5-l5 V/cm is suitable. As has been previously described, the state of electric charge of zinc oxide in a disperse system is the factor that determines which one of the two plates -electrodeposition plate and opposition plateis to be anode or cathode.

A suitable temperature for the electrodeposition is usually room temperature, for example, l025C. Although the rate of the electrodeposition increases with an increase in temperature, the resulting electrodeposited photosensitive layer (electrodeposition layer) is usually not smooth.

As for the photosensitive layer that has been formed by electrodeposition, when its thickness is 40 u and over, pinholes tend to be formed with resultant loss in gloss, and its electrophotographic characteristics therefore tend to beunsatisfactory. Desirably, the thickness of the photosensitive layeris less than 40 ,u. Under the condition such as mentioned above, the best result is obtained by carrying out the electrodeposition for 10-240 seconds.

3 The following examples are illustrative of the practices of this invention.

EXAMPLE 1 Photoconductive zinc oxide (made by Sakai Chemical lndustry Co., Ltd), acrylic resin (trademark RRA 401; made by Japan Reichhold lnc.), toluene and sensitizer (Rose Bengale) were mixed in the following amounts and proportions and the resulting disperse systems were prepared by mixing in a ball mill for 1 hour:

Sample No. zinc oxide resin toluene Rose Bengale l 100 g g zoo cc so mg l5 2 do. 20 do. 400 do. do.

3 do. 20 do. 600 do. do.

4 do. 20 do. 800 do. do.

5 do. 20 do. l000 do. do.

6 do. 20 do. I200 do. do.

7 do. 20 do. 1500 do. do. 70 X do. 10 do. 700 do do, 9 do. l5 do. 700 do. do. l0 do. 20 do. 700 do. do. I I do. do. 700 do. do. l2 do. do. 700 do. do. 13 do. do. 700 do. do. 14 do. do. 700 do. do.

The disperse systems thus prepared were transferred to a tank for electrodeposition and the electrodeposition was carried out under the following condition:

temperature of disperse system l0-20C.

electrodeposition plate (cathode) aluminum plate opposite plate (anode) aluminum plate space between the electrodes 2 cm voltage (DC) 200 V 35 current density l m Amp/dm time of electrodeposition I00 see.

In this manner, photosensitive layers having a thickness of below 40 4 were formed on the aluminum plate. Upon the completion of electrodeposition, the aluminum plates on which a photosensitive layer had been formed were dried in air and then they were placed in an oven, at a temperature of l l0-l 20C., for the complete removal by vaporization of the solvent contained within the electrodeposited layer. Various propertiesof the electrophotographic materials prepared in this way were tested and measured, such as the thickness of the photosensitive layer, the adherence between the photosensitive layer and the support (aluminum plate), the uniformity of the composition of the photosensitive layer, especially the surface condition of the photosensitive layer (as to uniformity, roughness, flow) and other properties as the electrophotographic material. The results obtained were as follows:

In the cases of the samples containing a little amount of toluene in the listed samples 1-7, the photosensitive layer having higher light sensitivity was obtainable, while the surface of the layer was neither smooth nor glossy. As the amount of toluene in the disperse system was increased. the surface condition ofthe photosensi tive layer was improved. In addition, the rise up rate of the surface potential of the layer became faster and the saturated surface potential of the layer increased. On the other hand, the electrodeposition rate became lower and the discharge rate by exposure of the photosensitive layer which has been formed became considerably slower. In due consideration of these points, the

-4 satisfactory result was obtained from the foregoing samples 2-5, namely, those having the toluene content of 400-1 ,000 cc.

As regards the samples 8-14, the relationship between the amount of the resin in the disperse system and the properties of the photosensitive layer was investigated and it was found that the satisfactory result is obtained by using the samples 9-l2, namely, those having the resin content of 15-30 g.

The effects of Rose Bengale, as sensitizer, in the disperse system prepared from g of zinc oxide, 20 g of acrylic resin and 800 cc of toluene were studied by adding from 0 mg to 100 mg of Rose Bengale to the disperse system and it was found that when the amount of the sensitizer in the disperse system was increased, its content in the electrodeposited photosensitive layer became larger and the sensitivity of the photosensitive layer was enhanced, but on the other hand, there are disadvantages that the fatigue of the photosensitive layer due to pre-exposure became greater and its electrodeposition rate becamelower. An amount of Rose Bengale in the disperse system in the range of about 25-75 mg based on 100 g of zinc oxide, give satisfactory results.

A summary of the data obtained in the foregoing experiments is as follows:

An excellent electrophotographic material is obtained by carrying out the electrodeposition in the following manner.

Composition of the disperse system Current density Time of electrodeposition 10-240 sec.

There is produced an electrodeposited photosensitive layer having a thickness of 40 ,u. or less, possessing a uniform composition and a smooth surface. The photosensitive layer exhibited excellent adherence to the base plate and a high degree of hardness and resistance to abrasion as well as excellent electrophotographic characteristics. The electrodeposited layer shows a saturated surface potential of about three times in value, compared to that of photosensitive electrophotographic material made by the conventional application methods. Also, the discharge on the surface of the layer by exposure was about two times faster. When the electrophotographic material of this invention is used as an original for copying, because of its smooth surface, it gives a clear copy-image and because the adherence between the photosensitive layer and the base plate is good, even if continuously copied more than several hundred times, there is no separation or peeling-off of the photosensitive layer, giving a clear copy-image with constant density.

EXAMPLE 2 The procedure of Example 1 was repeated by employing other insulating resins as a substitute for an acrylic resin.

When an olefinic resin, for example, Picopale 100 (trademark of a product made by Esso-Standard Oil Co.) or a styrenated alkyd resin, for example, Rastrasol S 4440 (trademark of a product made by Dainippon Ink and Chemicals lnc.) was employed as an insulating resin, the same results as in Example 1 using an acrylic resin were obtained. But the most smooth surface of the photosensitive layer was obtained in the case where an olefinic resin was used.

EXAMPLE 3 1n the case where trichloroethane, methylene chloride, xylene, tetrachloroethylene, ethylene dichloride, heptane or octane was used as a dispersion medium instead of toluene, substantially the same results as that of Example 1 were obtained.

EXAMPLE 4 The procedure of Example 1 was repeated except that distilled water was used as a dispersion medium in place of the abovementioned organic solvents; an acrylic resin (trademark: RAE 54, made by Toa Gosei Kagaku KK) was used as an insulating resin; triethanolamine was added as an emulsifier in the proportion of 0.3 percent by weight to the amount of the resin; the plate to be electrodeposited is an anode and the opposite plate is a cathode, a voltage of 5-20 V being applied. ln this case, the abovementioned resin is dispersed in water, carrying negative charge. Consequently, zinc oxide adsorbed with this resin migrates to the anode and is electrodeposited on it. Thus, a photosensitive layer having a thickness of less than 40 ,u and an excellent property was formed on a surface of the supporter in the same manner as that of Example 1.

EXAMPLE 5 The procedure of Example 4 was repeated except that: a water-soluble resin (trademark Goseran; made by The Nippon Synthetic Chemical Industry Co., Ltd.) derived from vinyl acetate-crotonic acid, a watersoluble resin (trademark Watersol 1900; made by Dainippon Ink and Chemicals, Inc.) derived from an alkyd resin, or a water-soluble resin (trademark Sumirez Resin 613; made by Sumitomo Chemical Co., Ltd.) derived from a melamine resin was used as an insulating resin.

The abovementioned resins dissociate and form anions in water, so that zinc oxide adsorbed with these resins is electrodeposited on the anode in the same manner as that of Example 4.

The electrophotographic material thus obtained possessed substantially the same properties as that of Example EXAMPLE 6 Other material, such as paper may be utilized as a support and a photosensitive layer can be formed on its surface as follows. The paper, the electric resistance of the surface of which was reduced to lo fl-cm or less by subjecting it to electroconductive treatment, was closely attached to a metal plate and this plate was used as an electrodeposition plate. The abovementioned electroconductive treatment was accomplished by the application of a polymer such as polyvinyl alcohol to a surface of the paper. The procedures of Examples 1-5 were repeated except that the following voltage was applied to the electrodes according to the kind of a dispersion medium.

Dispersion medium Voltage Organic solvent 300-400 V/cm Water 50-100 V/cm Photosensitive layers possessing the properties similar to those obtained in the previous examples were prepared on paper.

Although emphasis has been placed in this disclosure on the electrodeposition of photoconductive zinc oxide particles associated to the resin onto an electroconductive substrate, such as a metal, other photosensitive particles alone or in a mixture with zinc oxide might similarly be deposited for the preparation of a photosensitive layer in accordance with this invention. Additionally, as indicated hereinabove, various electroconductive surfaces and substrates might be employed in the practice of this invention for the electrodeposition of a photosensitive layer or compositions thereon. Suitable such substrates include not only suitably prepared normally electrically insulating substrates, such as a paper substrate, having a surface coating of electrically conductive materials thereon, e.g., paper coated with a graphite or an electrically conductive metal, but also metal surfaces or substrates in addition to aluminum, such as gold, copper, silver, tin, magnesium and their alloys.

What is claimed is:

l. A method of producing a zinc oxide-containing photosensitive layer upon an electroconductive substrate which comprises forming a disperse system comprising finely divided photoconductive zinc oxide and for each g. of zinc oxide from about 15-30 g. of an electrically insulating resin in from about 400 1,000 cc, of liquid medium and electrodepositing said zinc oxide associated with said resin on the said substrate at a current density of from about 0.5-2 mAmp./dm at a temperature of from about l025C. to produce a photosensitive layer having a thickness of up to about 400 microns.

2. A method in accordance with claim 1 wherein said zinc oxide-containing photosensitive layer is deposited on said substrate to a thickness not greater than 40 microns.

3. A method in accordance with claim 1 wherein said disperse system comprises said resin, said liquid medium, and said photoconductive zinc oxide in the proportions 15-30 g of resin and 400-1,000 cc of liquid medium to 100 g of photoconductive zinc oxide.

4. A method according to claim 1 wherein said resin is selected from the group consisting of non-polar resins, acrylic resins, alkyd resins, melamine resins and vinyl acetate-crotonic acid resins.

5. A method in accordance with claim 1 wherein said liquid medium is selected from the group consisting of toluene, xylene, tetrachloroethylene, ethylene dichloride, heptane, octane, trichloroethane, methylene chloride and water.

6. An electrodeposited zinc oxide containing photosensitive layer comprising photoconductive zinc oxide particles together with an electrically insulating resin, the electrodeposited layer having a thickness not 8 zinc oxide together with an electrically insulating resin dispersed in a liquid medium, the ratio of zinc oxide to resin being from about :15 to 100:30, the proportion of liquid medium to zinc oxide being 400-l,000

cc. of liquid medium to 100 grams of zinc oxide. 

1. A METHOD OF PRODUCING A ZINC OXIDE-CONTAINING PHOTOSENSITIVE LAYER UPON AN ELECTROCONDUCTIVE SUBSTRATE WHICH COMPRISES FORMING A DISPERSE SYSTEM COMPRISING FINELY DIVIDED PHOTOCONDUCTIVE ZINC OXIDE AND FOR EACH 100 G. OF ZINC OXIDE FROM ABOUT 15-30 G. OF AN ELECTRICALLY INSULATING RESIN IN FROM ABOUT 400-1,000 CC. OF LIQUID MEDIUM AND ELECTRODEPOSITING SAID ZINC OXIDE ASSOCIATED WITH SAID RESIN ON THE SAID SUBSTRATE AT A CURRENT DENSITY OF FROM ABOUT 0.5-2 MAMP./DM2 AT A TEMPERATURE OF FROM ABOUT 10*-25*C. TO PRODUCE A PHOTOSENSITIVE LAYER HAVING A THICKNESS OF UP TO ABOUT 400 MICRONS.
 2. A method in accordance with claim 1 wherein said zinc oxide-containing photosensitive layer is deposited on said substrate to a thickness not greater than 40 microns.
 3. A method in accordance with claim 1 wherein said disperse system comprises said resin, said liquid medium, and said photoconductive zinc oxide in the proportions 15-30 g of resin and 400-1,000 cc of liquid medium to 100 g of photoconductive zinc oxide.
 4. A method according to claim 1 wherein said resin is selected from the group consisting of non-polar resins, acrylic resins, alkyd resins, melamine resins and vinyl acetate-crotonic acid resins.
 5. A method in accordance with claim 1 wherein said lIquid medium is selected from the group consisting of toluene, xylene, tetrachloroethylene, ethylene dichloride, heptane, octane, trichloroethane, methylene chloride and water.
 6. An electrodeposited zinc oxide containing photosensitive layer comprising photoconductive zinc oxide particles together with an electrically insulating resin, the electrodeposited layer having a thickness not greater than about 40 microns, the ratio of zinc oxide to resin being from about 100:15 to 100:30.
 7. A bath useful for the electrodeposition of a photosensitive zinc oxide-containing coating upon an electrically conductive substrate in contact with said bath, said bath containing finely divided photoconductive zinc oxide together with an electrically insulating resin dispersed in a liquid medium, the ratio of zinc oxide to resin being from about 100:15 to 100:30, the proportion of liquid medium to zinc oxide being 400-1,000 cc. of liquid medium to 100 grams of zinc oxide. 